Heretofore, as one example of techniques in this field, for example, Patent Document 1 listed below discloses a technique that a ring gear is press-fitted to a flange of a differential case, and after that, inner peripheral edges at both ends of the ring gear are fixed by caulking by caulking portions formed on both ends of the flange. Then, predetermined components as well as the ring gear are assembled to the case, and thereby a differential sub-assembly used for a power transmission mechanism of a vehicle is obtained.
FIG. 29 shows a partial perspective view of a ring gear 81 in a prior art. On inner peripheral edges at both ends of the ring gear 81, a plurality of notches 82 are formed as caulked portions to be caulked by a caulking portion of a flange. Heretofore, caulking of the ring gear 81 is performed in such a way that the caulking portion plastically flows in the notches 82. These notches 82 are formed inside the ring gear 81, and the ring gear 81 is caulked by press-widening the flange from inside to outside. Patent Documents 2 to 6 listed below are related to a technique of caulking metal components.